In an emergency situation, a patient is likely focusing on the shock of the emergency, and little else. A trip to the emergency room can save a life.

But it could also send patients into shock when the bill arrives, saddling them with thousands of dollars owed for using an out-of-network doctor.

These surprise medical bills have many experts concerned -- since few ER patients would pause to ask a doctor whether or not they're in network.

A new article from researchers at Yale report that many emergency room visits involve costly, out-of-network treatment.

The researchers studied more than two million visits to the emergency room.

On average, more than one in five doctors involved in the emergencies were out-of-network for that patient. In some communities, out-of-network doctors accounted for 89 percent of ER claims.

In these cases, insurance companies only paid a small portion of the bill.

Patients are left to shell out, on average, over $600.

In some states, laws protect patients from these surprise costs. But in many cases the charges are hard to avoid, a situation that unfortunately may leave those recovering from emergency situations with one more burden to bear.